Air driven electrical generators, when used aboard a projectile or a rocket, can experience flight altitude of 65,000 feet or higher. At these extreme high altitudes, the amount of pneumatic energy or mass flow is at a premium. This is due to the reduction of the density of air at such altitudes. Since the amount of electrical energy generated is a function of the mass flow that is available to the generator during flight, it is essential for the generator to operate at its designed efficiency during high altitude flight.
The efficiency of conversion of pneumatic energy to electrical energy has been found to depend largely on the geometrical parameters of the nozzle-resonator configuration. Ideally, to optimize the generator parameters during high altitude flight, a design study is performed in wind tunnel tests or flight tests. Such tests, however, are costly and time consuming.
One type of air driven generator is described in U.S. Pat. No. 3,772,541, issued on Nov. 13, 1973, to Campagnuolo et al. In this device air is caused to enter a nozzle in which a cylindrical plug is centrally located to form an annular orifice. The air discharging from the annular orifice impinges directly on the edge of a resonating cavity producing a multiple frequency edgetone. The column of air in the resonating cavity is thereby caused to vibrate at a frequency determined by the depth of the cavity. The changes in pressure within the resonating cavity cause a diaphragm forming an end of the cavity to pulsate inwardly and outwardly. A rod is attached to the diaphragm, and this rod transmits the vibrations of the diaphragm to a metallic reed which will then oscillate between a pair of magnetic pole pieces. The oscillations of the reed will induce an electromotive force into a coil. The electromotive force induced in the coil may be made available to provide energy to operate an external electrical circuit.